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The relation of age at first calving to butter-fat production in the first five lactations¹

University of Wisconsin

Abstract

This report is based on the calving and production records of 253 Holstein cows from 40 herds in Wisconsin Dairy Herd Improvement Associations. Only herds which had 3 or more cows with at least 5 normal lactations each were included. These cows averaged 366 ± 2 pounds of butterfat (uncorrected for age) in the first 305 days of lactation and the range of plus and minus one standard deviation from the mean is 281 to 452 pounds. The question asked of these data was: What effect does early as compared with late first calving have on a cow's subsequent production and mature weight?

The cows were divided into classes according to the ages at which they first calved. The average cumulative butterfat production (2 milkings per day basis) of the cows in each class is shown in table I.

There was an irregular tendency for production to increase as age at first calving increased.

¹ Paper from the Department of Genetics, Agricultural Experiment Station, University of Wisconsin, No. 207; published with the approval of the Director of the Station.

² National Research Council Fellow in Biological Sciences.